The only feature that not is implemented in this release is
the "netascii" transfer mode.

The start/1 function starts
a daemon process which listens for UDP packets on a port. When it
receives a request for read or write it spawns a temporary server
process which handles the actual transfer of the file.

On the client side
the read_file/3
and write_file/3
functions spawns a temporary client process which establishes
contact with a TFTP daemon and performs the actual transfer of
the file.

tftp uses a callback module to handle the actual file
transfer. Two such callback modules are provided,
tftp_binary and tftp_file. See
read_file/3 and
write_file/3 for
more information about these. The user can also implement own
callback modules, see CALLBACK FUNCTIONS below. A callback module provided by
the user is registered using the callback option, see
DATA TYPES below.

TFTP SERVER SERVICE START/STOP

A TFTP server can be configured to start statically when starting
the Inets application. Alternatively it can be started dynamically
(when Inets already is started) by calling the Inets application API
inets:start(tftpd, ServiceConfig), or
inets:start(tftpd, ServiceConfig, How),
see inets(3) for details.
The ServiceConfig for TFTP is described below in
the COMMON DATA TYPES
section.

The TFTP server can be stopped using inets:stop(tftpd, Pid),
see inets(3) for details.

The TPFT client is of such a temporary nature that it is not
handled as a service in the Inets service framework.

COMMON DATA TYPES

ServiceConfig = Options
Options = [option()]
option() -- see below

Most of the options are common for both the client and the server
side, but some of them differs a little. Here are the available
options:

The name or IP address of the host where the TFTP daemon
resides. This option is only used by the client.

{port, Port}

Port = int()

The TFTP port where the daemon listens. It defaults to
the standardized number 69. On the server side it may
sometimes make sense to set it to 0, which means that
the daemon just will pick a free port (which one is
returned by the info/1 function).

If a socket has somehow already has been connected, the
{udp, [{fd, integer()}]} option can be used to pass the
open file descriptor to gen_udp. This can be automated
a bit by using a command line argument stating the
prebound file descriptor number. For example, if the
Port is 69 and the file descriptor 22 has been opened by
setuid_socket_wrap. Then the command line argument
"-tftpd_69 22" will trigger the prebound file
descriptor 22 to be used instead of opening port 69.
The UDP option {udp, [{fd, 22}]} automatically be added.
See init:get_argument/ about command line arguments and
gen_udp:open/2 about UDP options.

Policy for the selection of the temporary port which is used
by the server/client during the file transfer. It defaults to
random which is the standardized policy. With this
policy a randomized free port used. A single port or a range
of ports can be useful if the protocol should pass through a
firewall.

Flag for automated usage of the tsize option. With
this set to true, the write_file/3 client will
determine the filesize and send it to the server as
the standardized tsize option. A read_file/3
client will just acquire filesize from the server by sending
a zero tsize.

{max_tsize, MaxTsize}

MaxTsize = int() | infinity

Threshold for the maximal filesize in bytes. The transfer
will be aborted if the limit is exceeded. It defaults to
infinity.

{max_conn, MaxConn}

MaxConn = int() | infinity

Threshold for the maximal number of active connections.
The daemon will reject the setup of new connections if
the limit is exceeded. It defaults to infinity.

{TftpKey, TftpVal}

TftpKey = string()TftpVal = string()

The name and value of a TFTP option.

{reject, Feature}

Feature = Mode | TftpKey Mode = read | write TftpKey = string()

Control which features that should be rejected. This is
mostly useful for the server as it may restrict usage of
certain TFTP options or read/write access.

{callback, {RegExp, Module, State}}

RegExp = string()Module = atom()State = term()

Registration of a callback module. When a file is to be
transferred, its local filename will be matched to the regular
expressions of the registered callbacks. The first matching
callback will be used the during the transfer. See
read_file/3 and
write_file/3.

Threshold for the maximal number of retries. By default
the server/client will try to resend a message up to
5 times when the timeout expires.

Functions

start(Options) -> {ok, Pid} | {error, Reason}

Options = [option()]

Pid = pid()

Reason = term()

Starts a daemon process which listens for udp packets on a
port. When it receives a request for read or write it spawns
a temporary server process which handles the actual transfer
of the (virtual) file.

If LocalFilename is the atom binary,
tftp_binary is used as callback module. It concatenates
all transferred blocks and returns them as one single binary
in LastCallbackState.

If LocalFilename is a string and there are no
registered callback modules, tftp_file is used as
callback module. It writes each transferred block to the file
named LocalFilename and returns the number of
transferred bytes in LastCallbackState.

If LocalFilename is a string and there are registered
callback modules, LocalFilename is tested against
the regexps of these and the callback module corresponding to
the first match is used, or an error tuple is returned if no
matching regexp is found.

If LocalFilename is a binary, tftp_binary is
used as callback module. The binary is transferred block by
block and the number of transferred bytes is returned in
LastCallbackState.

If LocalFilename is a string and there are no
registered callback modules, tftp_file is used as
callback module. It reads the file named LocalFilename
block by block and returns the number of transferred bytes
in LastCallbackState.

If LocalFilename is a string and there are registered
callback modules, LocalFilename is tested against
the regexps of these and the callback module corresponding to
the first match is used, or an error tuple is returned if no
matching regexp is found.

info(daemons) -> [{Pid, Options}]

Pid = [pid()()]

Options = [option()]

Reason = term()

Returns info about all TFTP daemon processes.

info(servers) -> [{Pid, Options}]

Pid = [pid()()]

Options = [option()]

Reason = term()

Returns info about all TFTP server processes.

info(Pid) -> {ok, Options} | {error, Reason}

Options = [option()]

Reason = term()

Returns info about a TFTP daemon, server or client process.

change_config(daemons, Options) -> [{Pid, Result}]

Options = [option()]

Pid = pid()

Result = ok | {error, Reason}

Reason = term()

Changes config for all TFTP daemon processes

change_config(servers, Options) -> [{Pid, Result}]

Options = [option()]

Pid = pid()

Result = ok | {error, Reason}

Reason = term()

Changes config for all TFTP server processes

change_config(Pid, Options) -> Result

Pid = pid()

Options = [option()]

Result = ok | {error, Reason}

Reason = term()

Changes config for a TFTP daemon, server or client process

start() -> ok | {error, Reason}

Reason = term()

Starts the Inets application.

CALLBACK FUNCTIONS

A tftp callback module should be implemented as a
tftp behavior and export the functions listed below.

On the server side the callback interaction starts with a call to
open/5 with the registered initial callback state.
open/5 is expected to open the (virtual) file. Then either
the read/1 or write/2 functions are invoked
repeatedly, once per transferred block. At each function call
the state returned from the previous call is obtained. When
the last block has been encountered the read/1 or
write/2 functions is expected to close the (virtual) file
and return its last state. The abort/3 function is only
used in error situations. prepare/5 is not used on
the server side.

On the client side the callback interaction is the same, but it
starts and ends a bit differently. It starts with a call to
prepare/5 with the same arguments as open/5 takes.
prepare/5 is expected to validate the TFTP options,
suggested by the user and return the subset of them that it
accepts. Then the options is sent to the server which will perform
the same TFTP option negotiation procedure. The options that are
accepted by the server are forwarded to the open/5 function
on the client side. On the client side the open/5 function
must accept all option as is or reject the transfer. Then
the callback interaction follows the same pattern as described
above for the server side. When the last block is encountered in
read/1 or write/2 the returned state is forwarded to
the user and returned from read_file/3 or
write_file/3.

If a callback (which performs the file access
in the TFTP server) takes too long time (more than
the double TFTP timeout), the server will abort the
connection and send an error reply to the client.
This implies that the server will release resources
attached to the connection faster than before. The
server simply assumes that the client has given
up.

If the TFTP server receives yet another request from
the same client (same host and port) while it
already has an active connection to the client, it
will simply ignore the new request if the request is
equal with the first one (same filename and options).
This implies that the (new) client will be served
by the already ongoing connection on the server
side. By not setting up yet another connection, in
parallel with the ongoing one, the server will
consumer lesser resources.

No new options may be added, but the ones that are present in
SuggestedOptions may be omitted or replaced with new
values in AcceptedOptions.

Will be followed by a call to open/4 before any
read/write access is performed. AcceptedOptions is
sent to the server which replies with those options that it
accepts. These will be forwarded to open/4 as
SuggestedOptions.

On the client side where the open/5 call has been
preceded by a call to prepare/5, all options must be
accepted or rejected.

On the server side, where there is no preceding
prepare/5 call, no new options may be added, but
the ones that are present in SuggestedOptions may be
omitted or replaced with new values in AcceptedOptions.

The callback function is expected to close
the file when the last file chunk is
encountered. When an error is encountered
the callback function is expected to clean
up after the aborted file transfer, such as
closing open file descriptors etc. In both
cases there will be no more calls to any of
the callback functions.

The callback function is expected to close
the file when the last file chunk is
encountered. When an error is encountered
the callback function is expected to clean
up after the aborted file transfer, such as
closing open file descriptors etc. In both
cases there will be no more calls to any of
the callback functions.

abort(Code, Text, State) -> ok

Code = undef | enoent | eacces | enospc

| badop | eexist | baduser | badopt

| int()

Text = string()

State = term()

Invoked when the file transfer is aborted.

The callback function is expected to clean
up its used resources after the aborted file
transfer, such as closing open file
descriptors etc. The function will not be
invoked if any of the other callback
functions returns an error, as it is
expected that they already have cleaned up
the necessary resources. It will however be
invoked if the functions fails (crashes).

LOGGER FUNCTIONS

A tftp_logger callback module should be implemented as a
tftp_logger behavior and export the functions listed below.